Dzhura I O, Naidenov V G, Lyubanova O P, Kostyuk P G, Shuba Y M
A. A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Kiev.
Neuroscience. 1996 Feb;70(3):729-38. doi: 10.1016/s0306-4522(96)83010-7.
Ca-channel currents expressed in Xenopus oocytes by means of messenger RNA extracted from rat thalamohypothalamic complex were studied using the double microelectrode technique. Currents were recorded in Cl(-)-free extracellular solutions with 40 mM Ba2+ as a charge carrier. In response to depolarizations from a very negative holding potential (Vh = -120 mV), inward Ba2+ current activated at around -80 mV, peaked at -30 to -20 mV and reversed at +50 mV indicating that it may be transferred through the low voltage-activated calcium channels. The time-dependent inactivation of the current during prolonged depolarization to -20 mV was quite slow and followed a single exponential decay with a time-constant of 1550 ms and a maintained component constituting 30% of the maximal amplitude. The current could not be completely inactivated at any holding potential. As expected for low voltage-activated current, steady-state inactivation curve shifted towards negative potentials. It could be described by the Boltzmann equation with half inactivation potential -78 mV, slope factor 15 mV and maintained level 0.3. Expressed Ba2+ current could be blocked by flunarizine with Kd = 0.42 microM, nifedipine, Kd = 10 microM, and amiloride at 500 microM concentration. Among inorganic Ca-channel blockers the most potent was La3+ (Kd = 0.48 microM) while Cd2+ and Ni2+ were not very discriminative and almost 1000-fold less effective than La3+ (Kd = 0.52 mM and Kd = 0.62 mM, respectively). Our data show that messenger RNA purified from thalamohypothalamic complex induces expression in the oocytes of almost exclusively low voltage-activated calcium channels with voltage-dependent and pharmacological properties very similar to those observed for T-type calcium current in native hypothalamic neurons, though kinetic properties of the expressed and natural currents are somewhat different.
利用双微电极技术，研究了通过从大鼠丘脑下丘脑复合体提取的信使核糖核酸在非洲爪蟾卵母细胞中表达的钙通道电流。在以40 mM Ba2+作为电荷载体的无Cl(-)细胞外溶液中记录电流。从非常负的保持电位（Vh = -120 mV）去极化时，内向Ba2+电流在约-80 mV时激活，在-30至-20 mV时达到峰值，并在+50 mV时反转，表明它可能通过低电压激活的钙通道传导。在长时间去极化至-20 mV期间，电流的时间依赖性失活相当缓慢，遵循单指数衰减，时间常数为1550 ms，且有一个维持成分，占最大幅度的30%。在任何保持电位下，电流都不能完全失活。正如低电压激活电流所预期的那样，稳态失活曲线向负电位移动。它可以用玻尔兹曼方程描述，半失活电位为-78 mV，斜率因子为15 mV，维持水平为0.3。表达的Ba2+电流可被氟桂利嗪（Kd = 0.42 microM）、硝苯地平（Kd = 10 microM）和浓度为500 microM的氨氯地平阻断。在无机钙通道阻滞剂中，最有效的是La3+（Kd = 0.48 microM），而Cd2+和Ni2+的区分性不强，其效力几乎比La3+低1000倍（分别为Kd = 0.52 mM和Kd = 0.62 mM）。我们的数据表明，从丘脑下丘脑复合体纯化的信使核糖核酸在卵母细胞中诱导表达的几乎完全是低电压激活的钙通道，其电压依赖性和药理学特性与在天然下丘脑神经元中观察到的T型钙电流非常相似，尽管表达电流和天然电流的动力学特性有所不同。
